The present invention generally relates to methods for manufacturing enhanced current sharing for coated conductor high temperature superconducting tapes and articles formed in accordance therewith.
Development efforts in the area of coated high temperature superconductors (xe2x80x9cHTSxe2x80x9d) thus far have been directed at production of single tapes, that is, tapes typically including a substrate that can be textured or untextured, one or more biaxially textured buffer layers, an epitaxial HTS layer, and cap layers. In particular, attempts have been directed toward the production of high current carrying tapes from single substrate layers. In an effort to improve the overall current carrying capability of those proposed single tapes, high temperature superconductor (HTS) films will need to be very thick or will have to be deposited on both sides of a single substrate. Additionally, the articles created utilizing such construction present an unfavorable architecture regarding several critical performance parameters, including critical stress or strain parameters.
The use of a single tape with a very thick superconducting layer will not be practical for commercial applications. This may in part be due to the likelihood of the HTS layer to fracture as the thickness of the HTS layer increases (i.e. a known reduction in fracture strength). It is also likely that thickness will be limited by difficulty in controlling texture, and hence performance, as the HTS layer grows.
While current carrying capability may be improved by depositing a superconducting layer on each side of the substrate, this approach suffers other potential drawbacks. For example, the handling and processing of such a tape will be difficult relative to a single sided tape. In addition, the HTS films for two sided tapes will be in the least favorable position for several critical performance parameters.
Moreover, the possible use of conductive buffer layers to provide for a current path between the HTS filament and the substrate has been discussed extensively. While this solution appears to be possible it is severely limiting. The choices of conductive materials are limited because they should provide chemical compatibility with the superconductor and the substrate, exhibit a lattice match that enables epitaxial growth from the substrate, provide a template for epitaxial superconductor growth and possess good mechanical and physical properties. This is especially true since the resistance at the interface between the buffer and any other layer will govern the current transfer. It is likely that this interfacial resistance will still be high relative to the bulk resistance of the conductive buffer layer. The growth of a native oxide layer from the substrate material, which further increases the resistivity between the substrate and the buffer layer, is also likely to occur.
In the context of HTS coated conductors, it would therefore be desirable to provide methods and articles that overcome the shortcomings associated with the prior art.
This invention relates to a practical superconducting conductor based upon biaxially textured high temperature superconducting coatings. In particular, methods for producing articles, and articles produced in accordance therewith, are described which provide improved current sharing, lower hysteretic losses under alternating current conditions, enhanced electrical and thermal stability and improved mechanical properties between otherwise isolated films in a coated high temperature superconducting (HTS) wire. The invention also provides a means for splicing coated tape segments and for termination of coated tape stack ups or conductor elements. The invention further relates to multilayered materials which include sensitive HTS operational layers that can have laminate materials layered onto the multilayered materials so as to achieve desirable electrical, magnetic, thermal and mechanical properties of the composite tape.
In one embodiment, a multi-layer high temperature superconductor is provided and includes first and second high temperature superconductor coated elements. Each element includes a substrate, at least one buffer deposited on the substrate, a high temperature superconductor layer, and a cap layer. The first and second high temperature superconductor coated elements are joined at the first and second cap layers. Alternatively, if cap layers are not present, the first and second HTS coated elements are joined with an intervening, typically metallic, layer between the two HTS layers.
In one aspect, the invention provides a multi-layer high temperature superconductor, including a first high temperature superconductor coated element, which includes a first substrate (which can be biaxially textured, for example, be deformation); at least one first buffer deposited on the first substrate (which can be metal oxides, for example cerium oxide and/or gadolinium oxide, and can further optionally include yttria stabilized zirconia, all of which can be epitaxially deposited); at least one first high temperature superconductor layer (which can include metal oxide, such as rare earth oxide, including (RE)Ba2Cu3O7-xcex4, wherein RE is selected from the group consisting of rare earth elements and yttrium, and xcex4 is a number greater than zero and less than one); and a first cap layer. The multi-layer high temperature superconductor also includes a second high temperature superconductor coated element, which includes a second substrate; at least one second buffer deposited on the second substrate; at least one second high temperature superconductor layer; and a second cap layer, where the first and second high temperature superconductor coated elements are joined at the first and second cap layers. The first or second substrates can include nickel, such as for example, nickel-chromium, nickel-copper, or nickel-vanadium alloys. At least two buffers, for example three buffers, can be sequentially deposited on the first substrate. The first cap layer can be deposited on the first high temperature superconducting layer. The first and second substrates, the first and second buffers, the first and second high temperature superconducting layers, and the first and second cap layers can independently be of substantially identical composition. Thus, the first and second high temperature superconductor coated elements can be of substantially identical composition. The the first and second cap layers can be continuously joined at their uppermost surfaces. Alternately, the first and second cap layers can be a single continuous layer. The superconductor can be in the form of a tape. The substrates can optionally be substantially untextured, and the buffers and high temperature superconductor layers can be biaxially textured. The first and second high temperature superconductor coated elements can be registered at their respective edges. The first and second high temperature superconductor coated elements can be offset along their lengths. At least one of the first and second cap layers can extend along the edge of at least the first and second high temperature superconductor coated element. The superconductor can include a multifilamentary structure, such as when the first and second high temperature superconducting layers are divided into a plurality of filaments. The superconductor can further include a stabilizer, where the first and second cap layers can be joined to opposing surfaces of the stabilizer.
In a further aspect, the invention provides another multi-layer high temperature superconductor, including a first high temperature superconductor coated element, which includes a first substrate; at least one first buffer deposited on the first substrate; at least one first high temperature superconductor layer; and a first cap layer. The superconductor also includes a second high temperature superconductor coated element, which includes a second substrate; at least one second buffer deposited on the second substrate; at least one second high temperature superconductor layer; and a second cap layer, where the first and second high temperature superconductor coated elements are joined with an intervening metallic layer.
In yet a further aspect, the invention provides a multi-layer high temperature superconductor, as described immediately above but without cap layers, where the first and second high temperature superconductor coated elements are joined with an intervening metallic is layer.
Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in-the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.